Biocompatible surfactin-stabilized superparamagnetic iron oxide nanoparticles as contrast agents for magnetic resonance imaging

We have reported the ability of Bacillus natto TK-1 to produce surfactin which shows strong antitumor activity and appears less toxic to the normal cells. This report describes the use of the natural surfactin to stabilize superparamagnetic iron oxide nanoparticles (SPION) which can serve as a sensitive contrast agent for magnetic resonance imaging (MRI). The results showed that the organic magnetic nanoparticles were transferred into water by the surfactin, without particles aggregation and size change. The formed nanoparticles have an average diameter of 8 nm with a narrow size distribution. MRI of the nanoparticles in water confirmed its contrast enhancement effect in T2-weighted sequences. Calculated r1 and r2 relaxivites, and also r2/r1 ratio indicate that the nanoparticles after surfactin stabilizing may be a good candidate as T2 contrast agent.